(1) Technical Field
The present invention represents an improvement in piezoelectric ultrasonic atomizers, particularly of the type having an atomizing surface at a tip of a reduced diameter amplifying probe at one end of a transducer and a coaxial fluid delivery channel extending from the other end of the transducer to the atomizing surface. Such a piezoelectric device was disclosed in the applicant's earlier patent no. U.S. Pat. No. 4,723,708 (Ser. No. 07/068,717) which is hereby incorporated by reference.
(2) Background Art
Piezoelectric ultrasonic atomizers are finding increasing use in industrial applications where liquid materials must be delivered in the form of a very fine spray or mist. The design and construction of such atomizers is described in U.S. Pat. No. 4,337,896 of BERGER et al. A typical arrangement is to sandwich a flat electrode between two disks of piezoelectric material, such as lead zirconate titanate, to form a driving element, and then to clamp the driving element between a cylindrical front amplifying horn and a cylindrical rear dummy section. The amplifying horn is provided with a reduced diameter probe having an atomizing surface at its tip. The amplification of vibrational amplitude obtained at the atomizing surface is approximately equal to the ratio between the respective cross-sectional areas of the cylindrical portion of the front horn and of the end of the probe.
In the type of atomizer shown in U.S. Pat. No. 4,337,896, the necessary clamping pressure on the driving element is obtained by providing circumferential flanges on the adjacent ends of the front and rear sections and sawing the flanges together with a circle of bolts. The flanges also provide an annular bearing area for compressing an elastomeric gasket ring, to prevent liquid spray from contacting the outer peripheries of the piezoelectric disks. The sealing effectiveness of such a gasket is an important factor in extending the operating life of the atomizer.
The electro-mechanical drive elements typically employed in an atomizer are vulnerable to the corrosive effect of the fluid being atomized. Improper sealing against the environment is a problem in the art. Typically, sealing rings have been employed to effect a seal. The U.S. Pat. No. 4,496,101 to NORTHMAN, for example, discloses the use of sealing rings in the front portion of the housing (66 in FIG. 1), but fails to disclose the use of cooperating groove structure therewith (such as the reference shows for the rear portion).